Cytochrome P-450 and monooxygenase activity in hepatic microsomes from N-phenylimidazole-treated rats

Repeated administration of N-phenylimidazole (PI) to rats (3 daily doses of 200 mumol/kg/day) enhanced hepatic microsomal cytochrome P-450 levels (approx. 130%) and aminopyrine N-demethylase (APDM) and aniline p-hydroxylase (APH) activities (approx. 140%); aryl hydrocarbon (benzo[a]pyrene) hydroxylase (AHH) and 7-ethoxycoumarin O-deethylase (ECOD) activities were not enhanced over control values under similar conditions. Spectral studies with PI-induced microsomes indicated that although type II PI-binding characteristics were similar to those observed in controls, the 427 nm/455 nm absorbance ratio of the type III dihydrosafrole metabolite-cytochrome P-450 complex was lower than that in control microsomes. The results suggest that the inducing characteristics of PI bear some resemblance to those of phenobarbital (PB).